Having an maximized window and simply clicking on one of the borders without resizing it makes the window manager think that is unmaximized, even though it haven't changed size. And brcause of that the maximize/unmaximize button looses it's effect since both the maximized and the unmiximed window are of the same size. This annoys me a lot since I always manage to click on the borders by misstake. :) Reproducible: Always Steps to Reproduce:
Fixed in svn xfce_4_2 branch and trunk.